Add build checksum files to .gitignore

- Add .build_checksum and .lib_checksum to .gitignore
- These are build artifacts created by publish.py for optimization
- Should not be tracked in version control as they are environment-specific
- Remove any existing checksum files from git tracking

Author: Taniya Mathur

.gitignore

@@ -4,6 +4,8 @@ build.toml
 model.tar.gz
 .checksum
 .checksums/
+.build_checksum
+.lib_checksum
 .vscode/
 .DS_Store
 dist/